Given the first n terms of the sequence {an} and Sn = an − 1 (a ≠ 0), then the sequence {an} () A. It must be an arithmetic sequence B. it must be an arithmetic sequence C. It must be an arithmetic sequence or an arithmetic sequence D. It is neither an arithmetic sequence nor an arithmetic sequence

Given the first n terms of the sequence {an} and Sn = an − 1 (a ≠ 0), then the sequence {an} () A. It must be an arithmetic sequence B. it must be an arithmetic sequence C. It must be an arithmetic sequence or an arithmetic sequence D. It is neither an arithmetic sequence nor an arithmetic sequence

① When a = 1, Sn = 0, and A1 = A-1 = 0, an = sn-sn-1 = (an-1) - (an-1-1) = 0, (n ＞ 1) an-1 = sn-1-sn-2 = (an-1-1) - (an-2-1) = 0, an-an-1 = 0, and the sequence {an} is an arithmetic sequence. ② when a ≠ 1, A1 = A-1, an = sn-sn-1 = (an-1) - (an-1-1) = an -